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It may be cheaper and more cost-effective for semitrailer trucks to use a single tire per axle side instead of the traditional two tires. But is it safe?

"We just don't know yet," said Norm Lindgren, assistant director of the Utah Department of Transportation. "That's one reason why we've banned the single tires on all overweight and overlength trucks, as well as trucks hauling hazardous materials."That ban has sparked considerable protest by some truckers who have already invested heavily in single tires but cannot use them because of the ban. The ban will remain in effect until UDOT has a chance to study the effects of single tires on safety, as well as their impact on highways.

A public hearing is scheduled 7:30 p.m. Monday in the State Office Building auditorium on the Utah Transportation Commission's decision to ban the single tires. Trucking and safety experts from around the nation are expected to attend.

"The entire nation is watching to see what happens in Utah," said Lindgren. "It's a problem everywhere, and the other states are looking to see how we handle it."

Single tires on semitrailer trucks are growing in popularity. They have been used in Europe and Australia for years, and American truckers are becoming devoted converts of the single-tire arrangement. The single tires, though somewhat wider than tires used in a dual-tire arrangement, reduce the overall weight of the vehicle and improve the truck's fuel economy.

The single tires also make maintenance easier, they are cheaper and they make handling the big rigs easier.

UDOT engineers are concerned because so little is known about the effects of the single tires on American highways. The narrower the tire, the more damage the trucks cause to the highways.

"It puts a lot more stress on the highways," Lindgren said. "But how much? It's an unknown factor. We also don't know how the single-tire arrangement will work on snow and ice, or how they react on a steep grade. And what does it do to their braking capacity?"

Current regulations allow single tires on legal-sized trucks that are neither overweight or overlength. But UDOT wants time to study the idea of single tires on those trucks that carry the larger, heavier and dangerous loads.

"UDOT isn't saying it won't work on Utah highways," Lindgren said. "What we're saying is we need time to see what the problems are and draft regulations to meet those concerns. At this point, we don't have enough information to protect the billions of dollars invested in state highways or the public traveling on those highways."

UDOT, in cooperation with multi-state organizations, should make a decision on single tires within a year. The ban is effective July 1 for carriers of hazardous materials, and July 1, 1989, for all overweight and oversized loads.